How those things interacts:
My clients go to my page, hosted on server1, there they are able to upload their campaing and the email list( a simple txt file, that have all the email address)

My server2, has a cron job, that I made with php, that keeps on reading the database of server1, until it found something to send, when it found it he start sending the mail campaign to each email address on the txt file, one by one.

That work fines, with no problem at all, even sometimes getting reject by yahho, since I have a great sending demand.

What I want is to use my server3 in team with my server2, like this:
My server2 cron job will read the txt list and when it get on postfix, postfix will handle sending the email with server2 or server3.

Is that possible, is postfix able to do that? Is there any solutions for it?